1. Field of the Invention
The present invention relates to fasteners and, more particularly, to expandable fasteners for mounting to concrete structures, and the like.
2. Description of the Prior Art
Expandable anchors of many different types are already known. More particularly, expandable anchors have been developed for insertion into a hole formed in a support structure such that a cylindrical expansion sleeve of the anchor may be selectively expanded into frictional contact with the inside peripheral surface of the hole such that the anchor becomes frictionally anchored in the support structure. Typically, the expandable anchor includes an elongated expander member having a threaded first end and a flared second end opposite the first end with a cylindrical surface extending between the first and second ends around which there is provided the aforementioned expansion sleeve. The threaded first end is like a headless screw and extends outwardly of the support structure once the expandable anchor is positioned in the hole thereof. A nut threaded on the visible part of the threaded first end may be used as an actuating mechanism with an object to be secured to the support structure being typically located between the nut and the support structure as the threaded first end of the expandable anchor extends through this object. By rotating the nut, it engages the outer surface of the object and thus bears upon it such as to pull the expander member in an outward direction. As the expansion sleeve is already sufficiently frictionally engaged with the inside surface of the hole, when the expandable anchor is pulled by the rotation of the nut, the expansion sleeve stays substantially stationary in the hole and thus, as the expander member is pulled out of the hole, the flared second end of the expander member causes the cylindrical expansion sleeve to expand radially outwardly thereby increasing a friction between the expansion sleeve and the hole and thus further securing the expandable anchor therein.
Since the expansion sleeve must already be frictionally engaged with the hole before the expandable anchor is pulled, the outside diameter of the expansion sleeve must be similar to, even slightly greater than, the inside diameter of the hole in order to ensure an initial frictional contact therebetween which will then allow the expansion sleeve to remain still in the hole while the expander member is pulled outwardly thereof and thus allow the expansion sleeve to be expanded by the flared end of the expander member. This diameter of the expander member, at rest, results in that the expandable anchor when initially inserted in the hole must be inconveniently driven with significant force therein as the expansion sleeve is already frictionally engaged with the inside wall of the hole. The flared end then acts as a wedge to expand the expansion sleeve into greater frictional contact with the inside of the hole.
For instance, U.S. Pat. No. 2,647,431 issued on Aug. 4, 1953 to Lewis discloses an expansion bolt comprising a hollow shell having a leading end adapted to be expanded by a wedge into frictional contact with the peripheral wall of a hole. Resilient spurs, in some cases as part of a separate bail, are provided at opposite trailing ends of the shell, i.e. the end which is nearest to the opening of the hole, in order to engage the wall of the hole and prevent initial rotation of the shell relative to the hole until the shell frictionally engages the wall.
U.S. Pat. No. 3,250,170 issued on May 10, 1966 to Siegel, U.S. Pat. No. 3,620,120 issued on Nov. 16, 1971 to Warner, U.S. Pat. No. 4,337,012 issued on Jun. 29, 1982 to Sohnius, U.S. Pat. No. 4,403,894 issued on Sep. 13, 1983 to Clark, U.S. Pat. No. 5,028,188 issued to Jul. 2, 1991 to Prince and U.S. Pat. No. 5,344,257 issued on Sep. 6, 1994 to Wright et al. all disclose to expand a shell in a direction normal to a hole axis such that the periphery of the shell frictionally engages a wall of the hole. Notably, U.S. Pat. Nos. 3,620,120, 5,028,188 and 5,344,257 each describes having a resilient shell for facilitating the introduction of the expandable anchor within a hole while providing sufficient holding pressure to prevent the shell and associated wedge member from spinning in the hole as a torque is applied to a bolt for axially displacing the wedge member such as to radially expand the shell.
U.S. Pat. No. 2,783,673 issued on Mar. 5, 1957 to Lewis et al. and U.S. Pat. No. 5,352,066 issued on Oct. 4, 1994 to Schaeffer et al. also both disclose an expandable shell for facilitating the installation thereof within a hole. The leading end of the shell may be expanded at an angle with respect to the central axis of the hole.
Also known are undercut wedge anchors, wherein the hole formed in the support structure is enlarged with a tool at a distance from the visible opening of the hole such that the expandable undercut wedge anchor may thereafter be inserted in the hole until its expansion sleeve becomes located behind a shoulder defined at the junction of the enlarged area and the remainder of the hole. Once expanded, the expansion sleeve may abut this shoulder and thus retain the anchor in position in the support structure.